North American Network Operators Group

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Re: Level 3 RFO

  • From: Florian Weimer
  • Date: Mon Oct 24 12:39:58 2005

* Daniel Roesen:

> On Mon, Oct 24, 2005 at 01:25:23PM +0200, Florian Weimer wrote:
>> >> Are there any configuration tweaks which can locally confine such an
>> >> event?  Something like the hard prefix limit for BGP, perhaps.
>> >
>> > JunOS:
>> > set protocols ospf prefix-export-limit <n>
>> > set protocols isis level <n> prefix-export-limit <n>
>> Wouldn't an import limit be better?
> We're talking link-state protocols here... they need to have the same
> view everywhere. The only thing you can limit is what you inject into
> the (IGP-)global view.

What a pity.  There isn't an ugly workaround, either?  There has to be
something that can be done, given the operational risk that is

Certainly, this adds a new dimension to the "distributed single point
of failure" concept. 8-(

>> If you've got a almost-fully-meshed MPLS core, export limits won't
>> really work, will they?
> I don't understand this question. What has MPLS to do with IGP route
> filtering?!?

It's the "almost fully-meshed" part.  In such a setup, a single router
which exceeds the limit can affect a large part of the the network,
even if other routers do not propagate the bogus data.

But as you say, if the limit you mentioned is just a local limit on
redistribution to the IGP for a single router, my point is moot--if
it's in the IGP, you lose because the limit does not apply to routes
which are received over the IGP.